Gravitar PCB repair

tillentprs

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Hello,

I just picked up a Gravitar board that the seller said was working. I plugged it in, and got no picture. The LED spot killer light on the monitor was also flickering. The player one and two lights were blinking and when I tried to start a game, it made sound effects like it was trying to play blind, and a few small dots and dashes appeared in the center of the screen, like it was trying to generate a display. I know it's not the monitor, as a plugged my Black Widow PCB back in the cabinet and that plays fine. I tried putting the board into test mode, and nothing happens at all when I do that. I'm guessing the vector generating circuitry is bad on the board. Is there anybody here who could diagnose the problem and fix it? If so, how much? Thanks!
 
Why not do some quick tests yourself?

Try to swap out the AVG chip for a known good one. Common failure. (This assumes it is indeed playing blind).

Visually check all socketed parts. Especially the ROMs.
 
As VC mentioned, if it has the original AVG chip (the large black 40-pin chip at location J9) it's almost certainly bad. Get a replacement from Biltronix or Arcadeshop.

Also, if the AVG is bad, it probably will not play blind. You also shouldn't hook it to a monitor in this condition, as it can damage it. The game board can output excessive voltages to the monitor when the AVG chip is bad.

If that doesn't do it, I repair them.
 
My AVG replacement, the BXAVG, is available. Description here.

Since your BW works fine, try swapping the AVG from that into your G board and see if that helps. Other parts that you can swap from your BW board are the POKEYs, the CPU, and even the full set of EPROMs. That would be the fastest way to see if the G board could be fixed by replacing any of those socketed parts. Just be careful not to bend any chip pins or to plug in any chips backwards.

Bill B.
 
Why not do some quick tests yourself?

Try to swap out the AVG chip for a known good one. Common failure. (This assumes it is indeed playing blind).

Visually check all socketed parts. Especially the ROMs.

Thanks, but I should've mentioned that the G board already came shipped with the AVG upgrade kit from Clay Cowgill already installed. I could try taking that out and putting in the AVG chip from my Black Widow board.
 
Though parts do randomly fail when the PCB is powered up (here AVG and POKEY ICs are notorious), I would think the shaking during shipping might have dislodged a socketed part OR a part was damaged if not packaged well.

So the CC AVG is the TTL version, right? Looks like this?

This has two diagnostic LEDs ... what are they doing??

http://www.multigame.com/AVG.html
http://www.multigame.com/137179.PDF

There are two LEDs on the board (D101 and D102). D101 lights when the address "increment"​
signal is asserted inside the vector generator. D102 lights when the address "clear" signal is​
asserted inside the vector generator.

... .If one or both are out, or too dim or too bright it will indicate a problem
with that section of the AVG


AVG_new_l.JPG
 
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My AVG replacement, the BXAVG, is available. Description here.

Since your BW works fine, try swapping the AVG from that into your G board and see if that helps. Other parts that you can swap from your BW board are the POKEYs, the CPU, and even the full set of EPROMs. That would be the fastest way to see if the G board could be fixed by replacing any of those socketed parts. Just be careful not to bend any chip pins or to plug in any chips backwards.

Bill B.

Thanks, I should've mentioned in my original post that the board came shipped with Clay Cowgills upgrade kit already installed. However, yours looks more advanced and smaller. I may take you up on that.
 
Though parts do randomly fail when the PCB is powered up (here AVG and POKEY ICs are notorious), I would think the shaking during shipping might have dislodged a socketed part OR a part was damaged if not packaged well.

So the CC AVG is the TTL version, right? Looks like this?

AVG_new_l.JPG

That's it, and yes, several chips as well as the avg kit were loose when I got the board. iressed all the chips down tightly, checking for any bent pins, and the board still didn't work.
 
You can also try powering up with the test mode switch turned on (as opposed to flipping it on after it's been powered up already.) You might see different behavior, and should watch the screen carefully to see if it flashes a picture quickly. As even if it's only brief, you may be able to see any error codes being displayed, which may give you more insight as to what's going on.
 
Though parts do randomly fail when the PCB is powered up (here AVG and POKEY ICs are notorious), I would think the shaking during shipping might have dislodged a socketed part OR a part was damaged if not packaged well.

So the CC AVG is the TTL version, right? Looks like this?

This has two diagnostic LEDs ... what are they doing??

http://www.multigame.com/AVG.html
http://www.multigame.com/137179.PDF

There are two LEDs on the board (D101 and D102). D101 lights when the address "increment"​
signal is asserted inside the vector generator. D102 lights when the address "clear" signal is​
asserted inside the vector generator.

... .If one or both are out, or too dim or too bright it will indicate a problem
with that section of the AVG


AVG_new_l.JPG

Okay, thanks for the info! I tried it out and the LED at D102 is lit and the LED at D101 is not lit. Incidentally, I installed the AVG kit on my Black Widow board to see if that was defective and the game works, so I know that it is not the problem. However, I did notice that the LED at D102 was bright and the one at D101 was dimmer when the AVG kit was installed on the Black Widow PCB.

What do I check next? I'm assuming that it's indicating that there's something wrong with the vector graphics area of the board and not a bad POKEY.
 
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You can also try powering up with the test mode switch turned on (as opposed to flipping it on after it's been powered up already.) You might see different behavior, and should watch the screen carefully to see if it flashes a picture quickly. As even if it's only brief, you may be able to see any error codes being displayed, which may give you more insight as to what's going on.

Hi, I tried your suggestion, and there's nothing on the screen, only a tone.
 
A constant low tone is indicative of a bad ROM. In this case either L7, M/N7, or N/P7.

See the manual for details, but you need to check your ROMs with a programmer, or get some replacements and try replacing them. You can try reseating them again also, and cleaning the sockets with DeOxit, but you really should find someone near you with a programmer, so you can test the ROMs.
 
Since there is now an indication of an EPROM failure, you could do what I said previously and swap the entire set of EPROM chips from your working BW board to the G board and that might prove that the G board is actually good and just needs a new EPROM chip or two. It is safe to swap the EPROMs (the entire set, not just one) because, except for a couple of very minor sound related components, the boards are the same. Your Black Widow PCB is actually a Gravitar PCB with a red sticker placed over the G name. While there are in fact certain types of board problems that can cause an EPROM to not be read correctly by the game, swapping the chip set is the fastest and easiest way to find out quickly whether or not such a problem exists. If you can see the board work with the BW EPROMs, then you'll know for sure that replacing the G EPROMs with new ones will solve your problem before you even buy them. Otherwise, you'll be just guessing and hoping.

Bill B.
 
Since there is now an indication of an EPROM failure, you could do what I said previously and swap the entire set of EPROM chips from your working BW board to the G board and that might prove that the G board is actually good and just needs a new EPROM chip or two. It is safe to swap the EPROMs (the entire set, not just one) because, except for a couple of very minor sound related components, the boards are the same. Your Black Widow PCB is actually a Gravitar PCB with a red sticker placed over the G name. While there are in fact certain types of board problems that can cause an EPROM to not be read correctly by the game, swapping the chip set is the fastest and easiest way to find out quickly whether or not such a problem exists. If you can see the board work with the BW EPROMs, then you'll know for sure that replacing the G EPROMs with new ones will solve your problem before you even buy them. Otherwise, you'll be just guessing and hoping.

Bill B.

Thanks for your help! I'll try that to at least eliminate that as the problem. I do want to add that I'm convinced that the game is playing blind, since I can hear the sound effects when I start a game. Also, it is trying to show the display on the screen, but it just appears as moving dots towards the center of the screen. So, would that still be a rom issue? I would assume that would be a display issue.
 
A constant low tone is indicative of a bad ROM. In this case either L7, M/N7, or N/P7.

See the manual for details, but you need to check your ROMs with a programmer, or get some replacements and try replacing them. You can try reseating them again also, and cleaning the sockets with DeOxit, but you really should find someone near you with a programmer, so you can test the ROMs.

I can swap out my Black Widow roms to try to see if the board works with the BW roms, but that won't tell me which one or ones are bad. Unfortunately, I don't know anyone with a programmer. Do you know where I can get a new rom set ?
 
You may very easily have multiple problems overlapping, which is common on any old vector game. There may be separate game board and monitor issues.

You can try increasing the brightness on your screen (using the SCREEN knob on the HV cage of the monitor), and see if the board is drawing more than you may be seeing.

But also be aware that you are putting your monitor at risk by operating it with a board that is not working properly. If the board malfunctions and draws vectors that are out of range of the screen, you will very easily blow your deflection board.

Also, you can get new ROMs at hobbyroms.com.
 
Maybe get back to basics and OP should confirm all the voltages are present ... in particular the +15V and -15V and 6.8V generated by the LDOs/Zener on the logic card ... which are specifically used to draw XOUT and YOUT vectors.

Are any ICs socketed already in the analog output section?
 
I wouldn't go beyond swapping the AVG. The OP bought this board as working. If it didn't they should be contacting the seller for a refund. Unless I am missing something?

Brian
 
As VC mentioned, if it has the original AVG chip (the large black 40-pin chip at location J9) it's almost certainly bad. Get a replacement from Biltronix or Arcadeshop.

Also, if the AVG is bad, it probably will not play blind. You also shouldn't hook it to a monitor in this condition, as it can damage it. The game board can output excessive voltages to the monitor when the AVG chip is bad.

If that doesn't do it, I repair them.

Hi there, thank you all for all your help and suggestions. I swapped out the avg, both pokeys, the CPU, and no change. I was going to do the roms from my Black Widow next, but noticed that some of the EPROMs chips on the Gravitar board are not socketed, and I don't feel like desoldering chips just to test them (plus I hate desoldering chips). I could just order a new rom set, but that seems like a waste of money if that doesn't solve my problem. So, Would you be able to fix it for me? If so, how much? You can private message me if you'd prefer. Thanks!
 
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